The present invention relates to a method for expanding perlite. The expanded product of the invention has advantageous properties for numerous uses and particularly as a filteraid.
Perlite is a silicious material of volcanic origin, which has a silica content greater than 65% by weight and a combined water content of about 2 to 5% by weight. In addition to silica and water, perlite contains variable quantities of compounds of aluminum, sodium and potassium among others.
When perlite in the form of particles is introduced into a flame, it is subjected to expansion, or "bursts" into a material of lighter weight and density. Generally speaking, the expansion or "bursting" is observed when perlite is heated to a temperature on the order of 760.degree. to 1315.degree. C., according to the origin of the perlite and its particle size. For purposes of the present invention, temperatures on the order of about 870.degree. to 1150.degree. C. are used.
As a general rule, unexpanded perlite ore has a density on the order of about 0.96 to 1.28 kg/dm.sup.3 while after expansion, this density is on the order of about 0.032 to 0.16 kg/dm.sup.3.
Various techniques are known for expansion of perlite and these conventional methods have met with varying degrees of success. By reason of the continuing rise in demand for expanded perlite of better quality at a lower cost, it is desirable to substantially increase the capacity of known expansion installations, without a substantial investment of capital.
One object of the present invention is to considerably increase the production of expanded perlite and also to improve the quality thereof.
Another object is to provide a method yielding products with improved water-permeability.
Still another object of the invention is to provide a method reducing normal losses to a minimum and diminishing the quantity of floating material produced.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the combinations particularly pointed out in the appended claims.